On-board seekers have been used with vehicles such as airborne vehicles for control purposes, such as guidance control. In certain applications, there is a desire to reduce the size of the seeker to accommodate reduced sized vehicles, such as miniaturized rockets and/or missiles. In some cases, for example, the vehicle can be a rocket or missile having a diameter of less than two inches.
On-board receivers operated at lower frequencies have components such as waveguides that are relatively large. Higher frequency receivers can have higher cost and atmospheric losses.
Passive airborne radio frequency receivers receive reflections from targets illuminated by external tracking radar, such as a ground radar transmitter. Semi-active laser (SAL) seekers receive target reflections from external laser illuminators, such as a launch platform laser illuminator associated with air-to-ground missiles.
Microwave-photonic receivers for high data rate wireless communication over wide bandwidths are known. For instance, a web page entitled “Microphotonic RF Receiver (1999-2004)”, available on the University of Southern California website at dept/engineering/eleceng/Adv_Network_Tech/Html/RFreceiver.html, discloses a microwave-photonic wireless communication system for use, for example, in WiFi applications.
The microphotonic receivers discussed employ microresonator discs. Microresonator discs capture laser light input through evanescent wave coupling from a coupling prism and optical fiber. Each microresonator disc modifies a laser signal cycling within its so called “whispering gallery mode” perimeter by radio frequency phase modulation coupled to the microresonator disc via a microstrip waveguide. The microstrip waveguide can be configured in a periodic ring formation bonded to the top and bottom perimeter of the disc known as a radio frequency electrode resonator. The phase modulation is converted to amplitude modulation, internally, by self-mixing, or externally, by a traditional Mach-Zehnder configuration. Modulated optical signals couple out of the microresonator disc through the same prism mechanism used for input.